NOX storage catalytic converters serve to absorb and store nitrogen oxides (NOX) which may be emitted, in particular, by diesel engines operating in a lean-burn combustion mode. In response to a NOX storage catalytic converter being saturated with nitrogen oxide molecules, an operating phase with a rich air/fuel ratio may be performed for a duration of typically a number of seconds in order to regenerate the NOX storage catalytic converter in what may be known as a regeneration phase. During this phase, the stored nitrogen oxide molecules may be released and converted into components such as nitrogen, carbon dioxide and water vapour for example. The frequency with which a regeneration of said type may take place may be dependent on the nitrogen oxide emissions of the internal combustion engine, the storage capacity of the NOX storage catalytic converter, and the temperature of the exhaust gases of the internal combustion engine.
Previous approaches for determining the suitable times at which a regeneration of the NOX storage catalytic converter is required encompass the estimation of the NOX loading as a function of the NOX emission rate and the storage capacity of the NOX storage catalytic converter. In such approaches, the NOX emission rate of the internal combustion engine may either directly measured by means of a NOx sensor or is estimated with the aid of a model. In a NOx model of this type, NOX concentrations measured in the exhaust gas of the internal combustion engine to be listed as a function of the operating state of the internal combustion engine (that is to say the engine speed and engine load), and corrected as a function of the coolant temperature and the composition of the recirculated exhaust gas.
The storage capacity of the NOX storage catalytic converter may be a function of the measured or estimated catalytic converter temperature and the estimated NOX loading. The suitable time for a termination of the regeneration phase in one approach may be determined using a lambda probe arranged downstream. According to another approach, it is also possible to use a model for determining the NOX conversion rate, with the regeneration phase being terminated when the calculated loading falls below a predefined threshold value. In order to realize an on-board diagnostic (OBD) function, a NOx sensor which is arranged downstream of the NOX storage catalytic converter may be used in order to signal when the NOX emissions exceed the prescribed limit values.
Several publications, for example U.S. Pat. No. 6,645,361 B1 and also for example the SAE publication “Thick Film ZrO2 NOX Sensor” by N. Kato et al., publication no. 960334 of the Society of Automotive Engineers, Inc., Reprint from Electronic Engine Controls 1996 (SP-1149), International Congress & Exposition, Detroit (Mich.), 26-29 Feb. 1996, disclose electro-chemical gas sensors which can be used for NOX determination.
FIG. 1 schematically shows an example of an electro chemical gas sensor, such as described in the above citations. Sensor 1 may include a first chamber 2 connected to a second chamber 3 via a duct which extends through a diffusion barrier layer 4. A constant predetermined oxygen partial pressure is generated in the first chamber 2 by pump electrodes 5 by way of the supply or discharge of oxygen. The gas which is supplied via the duct of the second chamber 3 is reduced by way of electrodes 6. Electrodes 6 are arranged in second chamber 3 and include a catalytic material, so as to generate nitrogen and oxygen, whereupon a pump voltage which is proportional to the NOX concentration is tapped off. In addition, a heating device 7 is provided, to increase the temperature of the chambers or the pump electrodes to approximately 600° C. to 700° C. resulting in more efficient operation, and which can be surrounded for example by an insulating Al2O3 layer.
In one approach, in order to determine the NOX loading of a NOX storage catalytic converter, two NOx sensors may be used, one of which is arranged upstream of the NOX storage catalytic converter and the other of which is arranged downstream of the NOX storage catalytic converter.
However, the inventors have recognized that there may be several issue with such an approach. In particular, using two sensors to determine NOX loading of the NOX storage catalytic converter may result in considerable technical expenditure and corresponding costs with regard to the required provision of the corresponding monitoring device for the loading state.
Thus, it is an object of the present disclosure to provide a device for estimating the load state of an emission control device, such as a NOX storage catalytic converter, which permits reliable determination of the state of the device, such as the NOX load, with reduced technical expenditure and a corresponding reduction in cost. Note that the approach may applied to determining other loadings of an emission control device, such as oxygen loading, particulate matter loading, reductant loading, etc.
In one approach described herein, at least some of the above issues may be addressed by a device for estimating the loading state of a NOX storage catalytic converter, comprising: a module for determining the oxygen concentration difference between an oxygen concentration present in the exhaust gas upstream of the NOX storage catalytic converter and an oxygen concentration present in the exhaust gas downstream of the NOX storage catalytic converter, and a controller for estimating the loading state of the NOX storage catalytic converter on the basis of said oxygen concentration difference.
By determining the loading state of the NOX storage catalytic converter directly based on the oxygen concentration difference between an oxygen concentration which is present in the exhaust gas upstream of the NOX storage catalytic converter and an oxygen concentration which is present in the exhaust gas downstream of the NOX storage catalytic converter, the expenditure for actuating, heating, and for processing and evaluating the signals for two separate sensors which measure absolute oxygen concentration at different locations may be condensed to a single module. In this way, a significant reduction in the technical expenditure and associated costs may be obtained.
In addition, the estimation of the loading state of the NOX storage catalytic converter directly on the basis of the oxygen concentration difference has measurement-related advantages as a result of the significant reduction in the absolute measuring error which can be obtained in the case of a difference measurement in comparison to an absolute value determinations. In this way, the accuracy of the determination of the loading state of the NOX storage catalytic converter may be improved.
Further, the present application also contemplates a system for an engine, comprising: a unitary sensor communicating with exhaust gas at at least a first and second position in an exhaust of the engine, the sensor responsive to gas concentrations of the first and second positions; and a controller for adjusting engine operation responsive to the unitary sensor. The controller may adjust fuel injection, air-fuel ratio, estimation of catalyst NOx and/or oxygen loading, diagnostics, etc. The gas concentrations may include NOx, oxygen, etc. Also, the first and second positions may be upstream and downstream of an emission control device, respectively. Alternatively, the first and second positions may be in two separate exhaust conduits coupled to separate engine banks. Still other positions may also be used.